Braking systems, such as air brake systems, have generally been used to control movement of motor vehicles in a safe and effective manner. In particular, air brakes are commonly used on commercial vehicles such as trucks, trailers, and buses, which typically have large gross vehicle weights. The considerable inertial mass of these heavy-duty vehicles in combination with the high speeds at which they travel often requires a braking system which responds rapidly with substantial braking power. One system component which may be instrumental in the operation of air brake systems is the brake actuator. The brake actuator typically provides the necessary force when braking the vehicle.
FIG. 1 depicts a push rod generally known in the art. The push rod is a component of brake actuator 12 and is commonly found in many air disc brake systems. As shown, push rod 10 typically extends outwardly away from a mounting face 17 of brake actuator 12. The end of push rod 10 engages with ball end 16 of arm 14, typically a socket part of arm 14. Usually, the overall length L′ of push rod 10 and ball end 16 relative to mounting face 17 is important to proper braking. Because of such importance, the overall length L′ may be adjustable. Traditional braking systems, as illustrated in FIG. 1, often used shims 18, or spacers, placed between ball end 16 and push rod 10 to variably adjust overall length L′.
U.S. Pat. No. 5,579,873 to Kohar et al. (“Kohar”) relates to a brake actuator system having calipers that may close upon a disc in order to apply the brakes. Similar to the push rod of FIG. 1, Kohar may also use spacers to operate as shims in adjusting the calipers.
It is typically accepted and known that the overall length of the push rod and ball end relative to a mounting face surface of the actuator is usually essential to proper functioning of the brake system. If this length is too short, a user may need to apply the brakes in a more vigorous manner to brake the vehicle than if the overall length was properly determined. If the overall length is too long, the brakes may be applied continuously or when a user does not wish the vehicle to be braked, which may cause premature wear on the brakes. Because of the importance of the overall length, using shims to variably adjust the overall length may negatively affect accurate determinations of this length, which may possibly affect braking performance.
Usually, the overall length is determined within an acceptable tolerance range. Similarly, the components that make up the overall length, namely the push rod, ball end, and any shims used, are also typically manufactured within a known tolerance range. Combining the components typically results in the combination of the tolerances of the individual components to determine the overall tolerance range. This combination of the tolerances is known in the art to be defined as a “tolerance stack up”. The more shims used, the larger the overall tolerance range may become. In some instances, especially where an accurate determination of the overall length is desired, the resulting tolerance stack up may be larger than the acceptable tolerance range for the overall length, resulting in the overall length to be out of tolerance. Furthermore, variability in the actual dimensions of the components that results in an out of tolerance overall length may necessitate provisions for adjustments in order to bring the overall length back within tolerance, such provisions in turn may contribute to tolerance stack up.
Another disadvantage of using shims is that it may increase set up time for positioning the push rod relative to the ball end. The more shims involved to position the push rod relative to the ball end, the more time is typically needed to choose the correctly sized shims or interchange shims. Furthermore, if components of the braking system are interchanged, such as parts of the brake actuator, the shims may shift out of position, thereby necessitating repositioning of the push rod relative to the ball end. This problem may be exacerbated if the combination of shims chosen are not suited to the components of the braking system, where variability between braking systems sometimes favor particular combinations of shims. Adhering the shims to one another may reduce set up time but may also exacerbate tolerance stack up due to the adhesive material now being placed between the shims and affecting the overall length.
What is desired, therefore, is a push rod and ball end assembly that provides an accurate determination of the overall length relative to the mounting face surface. Another desire is a push rod and ball end assembly that reduces tolerance stack up. A further desire is a push rod and ball end assembly that reduces variability in overall length caused by tolerance stack up. Still another desire is a push rod and ball end assembly that reduces set up time.